As for the greenhouse gas (GHG) emissions from ocean-going vessels, United Nations Framework Convention on Climate Change (UNFCCC) had requested the International Maritime Organization (IMO) to estimate the emissions quantitatively and study available options for its reductions. In MEPC46, we reached an agreement to deliberate on the details of GHG emissions reduction from MEPC47 in the newly established WG.

In Japan, the Ship & Ocean Foundation (SOF), a think-tank concerned with ships and oceans, has worked on this issue. Interim findings of the research study have been reported in MEPC44/INF.10, MEPC45/INF.27 and MEPC46/INF.33. This document presents a summary of the final findings of the study so as to facilitate the deliberations by the WG.

CO 2 , CH 4 , N 2 O, HFCs gases were addressed as GHGs from ocean-going vessels. Total GHG emissions in 1997 were estimated and a breakdown of the CO 2 emission by vessel type (tanker, bulk carrier, container ships), vessel size (DWT or TEU) and vessel age were also estimated.

According to the estimation, the total GHG emissions from ocean-going vessels were approximately 400x10 6 t (CO 2 equivalent value) as shown in Table 1. CO 2 covers 96 to 97% of the total amount of the 4 gases, of which a breakdown for each vessel type was 28% for tankers, 30% for bulk carriers and 36% for container ships (shown in Table 2). Also, a breakdown for vessel size and vessel age of each vessel type was calculated as shown in Figure 1. On the other hand, GHG emissions excluding CO 2 (CH 4 , N 2 O, HFCs) contribute 3 to 4 % of the total. The issue on whether or not CH 4 emissions during loading and unloading of cargo and HFCs leakage from refrigerated/reefer containers during repair and maintenance be addressed as 'emissions from ocean-going vesselsf, must be deliberated by the WG.

The results of the estimation are shown in Figure 2. The CO 2 emission is estimated to be 20-44% increase in 2010 and 38-74% increase in 2020, than the emission in 1997. Looking at each vessel type, increase in CO 2 emission from container ships is higher than that from tankers or bulk carriers and it will constitute nearly half of the emissions from all ocean-going vessels in 2020. The result indicates the importance of taking emission reduction measures to container ships in terms of the prevention of global warming.

Even though quantitative estimation on the future emission trends of GHGs other than CO 2 were not carried out, as to HFCs, if we consider the possibility of an increase in the distribution of refrigerated/reefer containers due to the increasing traffic of processed foodstuffs, the considerable increase in future HFCs leakage can be anticipated. It is conceivable that together with CO 2 emission reduction from container ships, HFCs leakage reduction from refrigerated/reefer containers will become a more important subject in the future.

First of all, considerable studies have been done for the reduction of fuel consumption per transport unit of international shipping that is supposed to be the most cost-effective means of massive transport. Also taking into account future NOx restriction on ship engines, etc., it seems difficult to achieve additional large amount of CO 2 emission reduction in a short term by improvement of fuel consumption per transport unit. Under this circumstance, improvement technologies of propeller system shown in Table 3 can be considered as a relatively probable technology. Especially, Propeller Boss Cap Fin (PBCF) has an advantage of wider applicable scope for many type of vessels, possibility of retrofit, etc. As for mid-and long-term, CO 2 emission reduction technologies such as development of engines for alternate fuels (LNG, hydrogen, etc.) and modernized wind-powered ships, the viscous resistance reduction by micro-bubble technology, etc., can be considered.

Next, a number of reduction scenarios regarding CO 2 gas were assumed based on the direction of reduction policies and technology, and the effects were quantitatively evaluated (Table 4).

The results from calculations are shown in Table 4. By the year 2020, a 26.7 x 10 6 t (5%) of annual CO 2 emission reduction as compared to the base case becomes possible from the reduction technologies available for introduction in a short term, such as PBCF etc. However, the improvement of energy efficiency due to these reduction technologies will be cancelled out by surpassing the increase of the international shipping volume with the growth of the world economy, and the total amount of CO 2 emission will increase by 31.4% as compared to that of 1997. On the other hand, the CO 2 emission reduction effect of low-speed navigation is very large, and it is theoretically possible to control the amount of CO 2 emission in 2020 to the 1997 level. However, low-speed navigation will clearly bring about deterioration in the transportation service, and will also impose a change in the production/distribution system and in human lifestyle. Moreover, it will bring about a slowdown in the world economy. It remains questionable whether this measure can be effectively implemented without incentives on low-speed navigation. Thus, careful investigation into this is needed.

Moreover, the promotion of the elimination of substandard vessels engaged by IMO is also important because it has a secondary effect to stimulate the substitution of obsolete vessels, which have less energy efficiency.